Fix source indexing in Qt Creator 4.3

Create a fake project, just for including the files compiled by ninja
in a qmake project that Qt Creator can index, but which we do not build.

Change-Id: I7b4fc7ba23090bddb49ee1e85f76f71fb33544e2
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>